Electrooptic display systems typically include an electrooptic element (e.g., the display material itself) and electrodes (either opaque or transparent) for applying control voltages to the electrooptic element. Such a system may also include a nonlinear element to allow for multiplexing of the address lines to the electrodes, and an insulating material between various layers of the display system. These components have been fabricated by a multitude of conventional processes. For versatility and convenience of manufacture, many recent efforts have focused on producing all components of such displays by deposition printing using, for example, screen or ink-jet printing apparatus. The use of printing techniques allows displays to be fabricated on a variety of substrates at low cost.
The conducting materials used for electrodes in display devices have traditionally been manufactured by commercial deposition processes such as etching, evaporation, and sputtering onto a substrate. In electronic displays it is often necessary to utilize a transparent electrode to ensure that the display material can be viewed. Indium tin oxide (ITO), deposited by means of a vacuum-deposition or sputtering process, has found widespread acceptance for this purpose. More recently, ITO inks have been deposited using a printing process (see, e.g., U.S. Pat. No. 5,421,926).
For rear electrodes (i.e., the electrodes other than those through which the display is viewed) it is often not necessary to utilize transparent conductors. Such electrodes can therefore be formed from a material such as a silver ink. Again, these materials have traditionally been applied using costly sputtering or vacuum deposition methods.
Nonlinear elements, which facilitate matrix addressing, are an essential part of many display systems. For a display of M×N pixels, it is desirable to use a multiplexed addressing scheme whereby M column electrodes and N row electrodes are patterned orthogonally with respect to each other. Such a scheme requires only M+N address lines (as opposed to M×N lines for a direct-address system requiring a separate address line for each pixel). The use of matrix addressing results in significant savings in terms of power consumption and cost of manufacture. As a practical matter, its feasibility usually hinges upon the presence of a nonlinearity in an associated device. The nonlinearity eliminates crosstalk between electrodes and provides a thresholding function. A traditional way of introducing nonlinearity into displays has been to use a backplane having components that exhibit a nonlinear current/voltage relationship. Examples of such devices used in displays include thin-film transistors (TFT) and metal-insulator-metal (MIM) diodes. While these types of devices achieve the desired result, both involve thin-film processes. Thus they suffer from high production cost as well as relatively poor manufacturing yields.
Another nonlinear system, which has been used in conjunction with liquid crystal displays, a printed varistor backplane (see, e.g., U.S. Pat. Nos. 5,070,326; 5,066,105; 5,250,932; and 5,128,785, hereafter the “Yoshimoto patents,” the entire disclosures of which are hereby incorporated by reference). A varistor is a device having a nonlinear current/voltage relationship. Ordinarily, varistors are produced by pressing various metal-oxide powders followed by sintering. The resulting material can be pulverized into particulate matter, which can then be dispersed in a binder.
Additionally, the prior art mentions the use of a varistor backplane to provide thresholding for a nonemissive electrophoretic display device; see Chiang, “A High Speed Electrophoretic Matrix Display,” SID 1980 Technical Digest. The disclosed approach requires the deposition of the display material into an evacuated cavity on a substrate-borne, nonprinted varistor wafer. Thus, fabrication is relatively complex and costly.
Some success has been achieved in fabricating electronic displays using printing processes exclusively. These displays, however, have for the most part been emissive in nature (such as electroluminescent displays). As is well known, emissive displays exhibit high power-consumption levels. Efforts devoted to nonemissive displays generally have not provided for thresholding to facilitate matrix addressing.